L. N. Zelenina

On the thermodynamic properties of germanium-iodide compounds

Abstract The syntheses of high purity GeI 2 and GeI 4 from the elements are described. The vapour pressure over solid germanium (II) iodide has been measured by the static method with a membrane-gauge manometer from T =550 K to T =650 K and the molar enthalpy and entropy of sublimation calculated by second-law and third-law methods. Enthalpy differences for solid and liquid GeI 2 were measured in the temperature interval (330 to 770) K by drop calorimetry. The temperature, enthalpy and entropy of melting of germanium (II) iodide were determined. The values of the standard molar thermodynamic properties for solid and liquid GeI 2 are presented from T =298.15 K to T =781 K. We have used the maximum likelihood method in the treatment of the data obtained together with previous reported values. On the basis of this work we recommend a set of standard enthalpies of formation and absolute entropies for the Ge–I compounds.

Thermal properties of volatile ruthenium(III) complexes

Complexes of ruthenium(III) with the following beta-diketone derivatives: 2,4-pentanedione (Ru(acac)3), 1,1,1,6,6,6-hexafluoro-2,4-pentanedione (Ru(hfac)3), and 2-methoxy-2,6-dimethyl-3,5-heptanedione (Ru(mdhd)3) were synthesized, purified, and identified by chemical analysis and melting points. By difference-scanning calorimetry (DSC) in vacuum the thermodynamic characteristics of melting processes were defined. Using the static method with quartz membrane zero-manometer, the temperature dependencies of saturated and unsaturated vapor pressure were obtained for Ru(hfac)3. The standard thermodynamic characteristics of vaporization processes enthalpy ∆HT* and entropy ∆S°T* were determined.

Novel N-Containing Precursors of Nickel(II) for Film Deposition by MOCVD

The synthesis of volatile nickel(II) complexes with Ncontaining ligands like R(O,N)C(CH3)CH2C(CH3)NR (R – H, radical group) was carried out in inert atmosphere. The substances were characterized by means of elemental analysis, IRand NMR-spectroscopy, melting point, mass spectrometry. The thermal behavior of the compounds in the solid state was investigated by the method of thermogravimetry and difference-scanning calorimetry (DSC) in vacuum and helium. The thermodynamic characteristics of the melting processes (m.p., ∆meltHm.p., ∆meltSm.p.) were also determined by DSC: m.p. 157.5 ± 2 and 247.2 ± 1,2oC, ∆meltHm.p. = 25 ± 2 and 41,7 ± 0,3 kDj/mol, ∆meltSm.p. = 58 ± 5 and 80,1 ± 1,2 Dj/mol K for Ni(N(Me)C(CH3)CHC(CH3)N(Me))2 and Ni(OC(CH3)CHC(CH3)NH)2 respectively. Using the Knudsen method with mass spectrometric registration of gas phase and static method with quartz zero-manometer the temperature dependences of saturated vapor pressure of complexes were studied, the standard thermodynamic parameters of enthalpy and entropy of sublimation process were determined (Fig.1). The standard thermodynamic parameters of ones of evaporation process were calculated from data on sublimation and melting processes. It was shown that complex with ketoamine ligand is more thermodynamically stable in solid state than diimine analogue whereas the last one is more volatile that O-containing compound. By means of in situ high temperature mass spectrometry the thermodecomposition process of Ni(N(Me)C(CH3)CHC(CH3)N(Me))2 vapor was studied in vacuum temperature range of destruction and gas byproducts were determined (Fig.2). At temperatures 130– 250oC the first step of decrease of ion current intensity for metal-containing ion is observed that is apparently connected with forming of oligomers on surface being accompanied by isolation of 2-methylamino-4methylimino-2-pentene to gas phase. The decomposition of just formed on surface structures is hypothetically beginning at temperatures upper 250oC and is accompanied by isolation of products pointed on Fig.2. to gas phase. On account of the analysis of temperature behavior of reaction products the scheme of mechanism of chemical transformation on heated surface was proposed. The complexes have been used as precursors for the Ni-containing film formation by Metal-Organic Chemical Vapor Deposition. The film decomposition conditions were chosen on the base of information about thermal behavior of complexes. The experiments were carried out in hydrogen at substrate temperature 320– 370oC. The films obtained were investigated by using different methods: SEM, XRD etc. 1,9 2,0 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9 -3,5 -3,0 -2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5 2,0

Thermal dissociation of intercalated titanium selenides Fe x TiSe 2 ( x = 0.10, 0.25, 0.50)

Using static tensimetry, the selenium pressure during dissociation of intercalated compounds FexTiSe2 has been measured in a temperature range of stability of the homogeneous material and in the region of decomposition caused by thermal expansion of the polaron band. It has been shown that covalent centers in the stability region of the homogeneous state, which are stabilized by the polaron state of conduction electrons, behave as the effective oxidants lowering the Fermi level. Broadening of the polaron band in the region of a high iron concentration leads to weakening the oxidizing influence of polarons. Iron selenides are formed during the decomposition of intercalated compounds, which leads to an essential non-quasi-binarity of the Fe-TiSe2 system.

Kinetics of reactions in interlayer space of titanium diselenide intercalated with iron

Decomposition of a homogeneous intercalation compound with the formation of inclusions in the interlayer space of a matrix lattice has been directly observed. In full compliance with previously advanced theoretical concepts, it has been shown that the decomposition is accompanied by metallic iron extraction, which then gradually transforms into iron selenide due to the interaction with gaseous selenium.The hierarchy of diffusion mobilities of various defects in FexTiSe2 intercalation compound has been determined. It has been found that the largest mobility is inherent to intrinsic defects of the TiSe2 lattice, i.e., vacancies in Ti and Se sublattices. The phenomenon of dissociation pressure oscillations as a function of time has been detected. This phenomenon has been explained by the existence of a slow decomposition stage, i.e., intercalated iron diffusion during the formation and dissolution of its inclusions as an individual phase.

Joint processing of experimental data on melting, evaporation, and sublimation processes

A technique and computational program for estimating thermodynamic parameters are developed for the joint processing of experimental data on the saturated vapor pressure in melting, evaporation, and sublimation processes. Computation is based on the equality of pressures over the solid and liquid phases at a melting temperature. The efficiency of the proposed technique is demonstrated by processing experimental data on the phase transitions of Sc(thd)3.

A calorimetric study of germanium dibromide

The temperature dependence of the heat capacity of germanium dibromide was studied over the temperature range 8.3–314 K by adiabatic calorimetry. The enthalpy of formation of solid germanium dibromide was determined by solution calorimetry. Scanning calorimetry was used to obtain the thermodynamic characteristics of fusion of GeBr2. The thermodynamic characteristics of the Ge-Br system studied by us earlier were used to consistently calculate the consistent standard enthalpies of formation and absolute entropies of germanium bromides in the solid, liquid, and gaseous states.

New praseodymium polyselenide PrSe1.95: Synthesis and X-ray diffraction study of crystals

By thermodynamic simulation of the Pr–Se–I system, the optimal growth conditions for new crystalline praseodymium polyselenide PrSe1.95, whose existence was proved in our previous works, are determined. Based on the obtained information, the PrSe1.95 crystals are grown by the vapor transport technique using iodine as the transport agent. The crystals produced are identified by microprobe and powder X-ray diffraction analysis. Single crystal X-ray diffraction shows that the crystals are not monophasic, but consist of blocks with tetragonal and monoclinic symmetries, which have a common structural prototype (PbFCl). For two different crystals cut out of a larger one, the structure is determined and the composition is refined. The results of powder and single crystal X-ray diffraction analyses of one of these crystals (monoclinic one) coincide.

The thermodynamic properties of talyl-and phenylsilanes

The enthalpies of fusion of C6H5SiH3, C6F5Si(CH3)3, and (C6H5)4Si were obtained in scanning calorimetry measurements. Pressure over the condensed talylsilane 4-CF3C6F4SiCH3, phenylsilane C6H5SiH3, and pentafluorophenylsilane C6F5SiCH3, (C6F5)2Si(CH3)2, and (C6F5)4Si phases was measured by the static method with the use of membrane null manometers. Equations approximating the dependences of saturated vapor pressures on temperature and the enthalpy and entropy of vaporization were obtained.

New gadolinium polyselenide GdSe1.89(6) in the PbFCl matlockite structure type

Optimal growth conditions for GdSe1.85 crystals are found by the thermodynamic simulation of the Gd–Se–I system. The obtained data are used to grow GdSe1.85 crystals by the vapor transport method using iodine as a transport agent. The grown crystals are identified by microprobe and powder XRD analyses. The structure is determined by the single crystal XRD analysis and the composition is refined. The crystal structure is in general typical of the structures of REM polychalcogenides, however, the unit cell represents the metric type unknown previously: a = 4.0562(2) Å, b = 8.1065(5) Å, c = 9.2489(5) Å, α = 115.9990(10)°, β = 90.000(2)°, γ = 89.9750(10)°, V = 273.34(3) Å3, Z = 4, dcalc = 7.659 g/cm3, space group Pb11. The experimental material for the single crystal XRD analysis is obtained on an automated Bruker X8 APEX diffractometer (MoKα radiation, graphite monochromator, CCD detector resolution 1024×1024 pixel, distance to the detector L = 50 mm, rotation about the φ axis 15 min) by the standard procedure, 2274 measured reflections, out of them 1523 independent (R(int) = 0.0352), R factor [I > 2σ(I)] = 0.0517, R factor (all measured) = 0.0694).